Non-luteal cells comprise a substantial volume of the corpus luteum, and macrophages are a prominent non-lutein cell type. Recently, macrophages have been recognized to have important functions in growing and differentiating tissues other than their role as phagocytes. The objective of this proposal is to characterize function and number of ovarian macrophages and to determine how these properties relate to changes in corpus luteum function. Three complementary approaches will be taken to study mononuclear phagocytes in luteal tissues. First, macrophages, isolated by collagenase dispersion of superovulated rat ovaries, will be assessed for their state of activation by measuring several functional properties, including phagocytosis, Fc and C3b mediated ingestion of opsonized sheep red blood cells, plasma membrane activity of 5'-nucleotidase, secretion of plasminogen activator, and metabolism of arachidonic acid to several members of the prostaglandin family. Changes in properties of ovarian macrophages will be related to the endocrine status of luteal tissue, and also compared to the functions of stimulated and unstimulated peritoneal macrophages. The second approach will determine whether secretory products of ovarian macrophages influence luteal cell function. Ovarian macrophages, obtained from luteal tissues at different times of the cycle, will be cultured, and the conditioned media from these cultures as well as media from cultured peritoneal macrophages will be added to cultures of luteinized rat granulosa cells. The effects of macrophage products will be determined by measuring alterations in progestin secretion, responses to gonadotropins, gonadotropin binding and ultrastructural appearance of the luteal cells. The third approach will assess the effect of the female sex steroids on the functions of cultured ovarian and peritoneal macrophages. With these studies we hope to establish roles for resident ovarian macrophages in the initiation of certain functional and structural alterations of the corpus luteum with particular emphasis on the period of corpus luteum formation, active steroidogenesis and initiation of functional luteolysis.